1. Field of the Invention
The invention relates to a door structure, comprising:
a first plate serving as fixed frame with an opening enclosed by a peripheral edge; and
a door connected pivotally to this first plate by at least one hinge construction such that with its peripheral zone the door can co-act sealingly with said peripheral edge;
which first plate carries a number of peripherally arranged clamps, which clamps are simultaneously rotatable by a collective operating mechanism with an operating handle and through rotation can co-act with the peripheral surfaces of corresponding non-round continuous holes in the door, which peripheral surfaces have for each clamp a contact surface inclining relative to the main plane of the door structure in the closed situation, which continuous holes have a form such that a clamp can pass therethrough.
2. Description of the Prior Art
A known door structure, such as that disclosed in PCT Publication No. WO-A-98/44228, was embodied such that it met high standards of resistance to fire and explosion. To this end the known door structure was embodied in mechanically very strong and non-deformable manner, whereby the sealing and mechanical integrity of the door structure was preserved even under extreme conditions.
It is an object of the invention relative to this prior art to provide a door structure which meets the higher standards of fire and explosion resistance.
With a view hereto, the door structure according to the present invention has the feature that the door comprises a second plate which is received in a framework which co-acts sealingly with the peripheral edge in the closed position;
the clamps are arranged symmetrically pairwise on rotation shafts;
the continuous holes in the door are correspondingly formed slotted holes;
each peripheral surface of a continuous hole in the door has two substantially symmetrically located, inclining clamp contact surfaces; and
the peripheral edge is deformable under the influence of an air pressure pulse acting on the door structure in the closed position such that at least the door can be pressed out of the main plane it occupies when at rest while maintaining the sealing co-action between the framework and the peripheral edge and the mechanical integrity of the door structure.
The advantage of the structure according to the invention lies in the fact that the use of mechanical strengthening as in the described prior art is dispensed with, whereby the door structure can be lighter and can be manufactured more cheaply.
A specific embodiment has the special feature that the peripheral edge comprises a plate part with a thickness substantially smaller than the thickness of the first plate. This smaller thickness has the result that the plate part, and therewith the peripheral edge, deforms relatively easily under the influence of an air pressure pulse which can occur for instance during an explosion.
The door construction can in particular have the special feature that the thickness of the plate part amounts to a maximum of 0.5 times the thickness of the first plate.
In accordance with yet another aspect of the invention, the door structure has the special feature that the second plate has a thickness substantially smaller than the thickness of the first plate such that the second plate is deformable in the manner of a membrane under the influence of said air pressure pulse.
This latter embodiment can be particularly characterized herein in that the thickness of the second plate amounts to a maximum of 0.3 times the thickness of the first plate.
The door structure preferably has the special feature that the peripheral edge comprises a plate part which has a substantially prismatic, general wave shape with at least one wave.
In order to prevent sharp transitions in the four corners, the embodiment is recommended in which the peripheral edge is angled in its four corners and thus takes the form of an octagon.
This latter variant is preferably embodied such that the angles of the octagon are (135xc2x120)xc2x0.
In order to ensure the sealing and mechanical integrity of the door structure, also under very extreme deforming conditions, use can be made of hooking means present on respectively the peripheral edge and the door peripheral zone which only enter into hooking co-action when a certain minimal deformation of the door structure is exceeded as a result of an air pressure pulse acting thereon.
For the best possible symmetrical loading of the structure and the avoidance of mechanical stresses, the door structure can preferably be embodied such that the clamps and the associated holes are placed symmetrically.
A very good combination of low cost and high quality is realized with an embodiment in which the door structure consists substantially of metal, for instance steel.
The term xe2x80x9csubstantiallyxe2x80x9d is understood to mean that the door structure may also comprise non-dominant components of a different composition. The door structure can for instance comprise thermal insulation material such as mineral wool. In addition, appropriate parts are generally provided with anticorrosive and protective coatings, while sealing means can for instance consist of rubber or rubber-like materials.
For the proper desired deformability under the said conditions, the door structure can be embodied such that the second plate consists of steel plate with a thickness of a maximum of 3 mm.
For the same reason the door structure can have the special feature that the plate part consists of steel plate with a thickness of a maximum of 5 mm.
A particular embodiment is characterized by a neoprene rubber sealing ring which seals the door relative to the first plate in closed situation.
A specific embodiment has the special feature that each clamp comprises a rotation shaft which is provided with screw thread and co-acts with a nut present on the peripheral edge such that a rotation of a clamp entails an axial displacement.
Depending on the orientation of the screw thread the axial displacement resulting from the action of the clamps can be enhanced or, conversely, prevented subject to the set requirements for the design. When the axial displacement is prevented by the clamps themselves, a greater clamping force can be realized, while in the other case a greater axial displacement is obtained.
A preferred embodiment has the special feature that each clamp is coupled via a transmission with a certain dead stroke to the collective operating mechanism. This structure prevents in all conditions possible spontaneous release of the clamps in the case where great bending occurs, which can be the case particularly in the case of explosive pressure loads. The described dead stroke in accordance with the above described final aspect of the invention prevents unintentional opening of the door in such conditions.